Two leading officials in charge of reviewing COVID-19 vaccine applications at the U.S. Food and Drug Administration (FDA) will step down this fall when the Biden administration prepares to offer vaccine booster shots to the public in September.

Marion Gruber—director of the FDA’s Office of Vaccines Research & Review, and Phil Krause—deputy director, will leave the agency in October and November, respectively, CNBC reported on Tuesday, Aug. 31, citing a letter from FDA spokeswoman Stephanie Caccomo.

In the letter, Dr. Peter Marks, the FDA’s top vaccine regulator—sent thanks to Marion and Phil for their contribution to the agency.

The reason behind their resignations, according to Endpoints News—a biotech industry publication, is that the two senior FDA vaccine regulators are frustrated at the Centers for Disease Control and Prevention (CDC) and its advisory committee for their involvement in decisions they think should be up to the FDA.

The final straw was when the Biden administration got ahead of the agency on COVID-19 vaccine booster shots, according to a former senior FDA leader.

The Department of Health and Human Services (HHS) officially announced on Aug. 18 that the booster shots for COVID-19, by Pfizer and Moderna, would be available to all adult Americans by September 20. 

President Joe Biden revealed on Aug. 27 that he and his chief infectious disease advisor Dr. Anthony Fauci had discussed the requirement of a COVID-19 booster shot for every five months.

While the Biden administration is scheduled to deliver the booster shots to the general public later this month, some health experts saw the move as premature and political, especially because the FDA has not finished reviewing data on boosters yet.

At a news briefing on Tuesday, when asked whether the FDA officials’ departures would affect the agency’s trust, White House COVID-19 czar Jeff Zients said the decision to distribute boosters was made by a number of senior health officials, including acting FDA Commissioner Dr. Janet Woodcock.